Cancer is a serious public health problem in the United States and other developed countries. Currently, one in four deaths in the United States is due to cancer. Cancer therapy involves treating patients with chemotherapeutic drugs to kill tumor cells. However, subsets of tumor cells are frequently resistant to drug therapy and survive to re-populate at sites of origin and at distant metastatic sites, leading to detectable disease recurrence and morbidity. Many carcinoma tumor cells that have the properties of increased invasive and metastatic capacity, and altered drug resistance, are thought to have undergone a morphological transformation encompassing or similar to EMT (epithelial-mesenchymal transition). Cells undergoing EMT lose the normal adhesive properties of epithelial cells and undergo a spectrum of changes including loss of E-cadherin expression and expression of mesenchymal markers, increased motility, increased invasiveness, and increased resistance to cell death.
The leading therapies for cancer are currently surgery, radiation and chemotherapy. Chemotherapeutic approaches such as anti-tumor antibiotics, alkylating agents, nitrosourea compounds, vinca alkaloids, steroid hormones, and anti-metabolites form the bulk of therapies available to oncologists. Despite advances in the field of cancer treatment, cancer remains a major health problem.
Angiogenesis, the formation of new blood vessels out of pre-existing capillaries, is a sequence of events that is of key importance in a broad array of physiologic and pathologic processes. Normal tissue growth, such as in embryonic development, wound healing, and the menstrual cycle, is characterized by dependence on new vessel formation for the supply of oxygen and nutrients as well as removal of waste products. A large number of different and unrelated diseases are also associated with formation of new vasculature. Among certain pathologies are conditions in which angiogenesis is low, and should be enhanced to improve disease conditions. More frequently, however, excessive angiogenesis is an important characteristic of various pathologies, including pathologies characterized or associated with an abnormal or uncontrolled proliferation of cells. Pathologies which involve excessive angiogenesis include, for example, cancer (both solid and hematologic tumors), cardiovascular diseases (such as atherosclerosis and restenosis), chronic inflammation (rheumatoid arthritis, Crohn's disease), diabetes (diabetic retinopathy), psoriasis, endometriosis, neovascular glaucoma and adiposity (3). These conditions may benefit from chemotherapeutic inhibition of angiogenesis.
Generally speaking, the angiogenic process entails the proliferation and migration of a normally quiescent endothelium, the controlled proteolysis of the pericellular matrix, and the synthesis of new extracellular matrix components by developing capillaries. The establishment of new intra- and intercellular contacts and the morphological differentiation of endothelial cells to capillary-like tubular networks provide support for their subsequent maturation, branching, remodeling and selective regression to form a highly organized, functional microvascular network. The autocrine, paracrine and amphicrine interactions of the vascular endothelium with its surrounding stromal components, as well as with the pro-angiogenic and angiostatic cytokines and growth factors orchestrating physiologic angiogenesis, are normally tightly regulated both spatially and temporally.
Angiogenesis is crucial to the growth of neoplastic tissues. For more than 100 years, tumors have been observed to be more vascular than normal tissues. Several experimental studies have suggested that both primary tumor growth and metastasis require neovascularization. In contrast to the well orchestrated process described above for normal tissue growth, the pathologic angiogenesis necessary for active tumor growth is generally sustained and persistent, with the initial acquisition of the angiogenic phenotype being a common mechanism for the development of a variety of solid and hematopoietic tumor types. Tumors that are unable to recruit and sustain a vascular network typically remain dormant as asymptomatic lesions in situ. Metastasis is also angiogenesis-dependent: for a tumor cell to metastasize successfully, it generally must gain access to the vasculature in the primary tumor, survive the circulation, arrest in the microvasculature of the target organ, exit from this vasculature, grow in the target organ, and induce angiogenesis at the target site. Thus, angiogenesis appears to be necessary at the beginning as well as the completion of the metastatic cascade.
The criticality of angiogenesis to the growth and metastasis of neoplasms thus provides an optimal potential target for chemotherapeutic efforts. Appropriate anti-angiogenic agents may act directly or indirectly to influence tumor-associated angiogenesis either by delaying its onset (i.e., blocking an “angiogenic switch”) or by blocking the sustained and focal neovascularization that is characteristic of many tumor types. Anti-angiogenesis therapies directed against the tumor-associated endothelium and the multiple molecular and cellular processes and targets implicated in sustained pathologic angiogenesis are being actively evaluated for their safety and efficacy in multiple clinical trials. However, there has been limited success to date with the discovery and/or identification of safe and/or effective anti-angiogenic agents.
Fibrosis is the abnormal accumulation of fibrous tissue that can occur as a part of the wound-healing process in damaged tissue. Such tissue damage may result from physical injury, inflammation, infection, exposure to toxins, and other causes.
Liver (hepatic) fibrosis, for example, occurs as a part of the wound-healing response to chronic liver injury. Fibrosis occurs as a complication of haemochromatosis, Wilson's disease, alcoholism, schistosomiasis, viral hepatitis, bile duct obstruction, exposure to toxins, and metabolic disorders. This formation of scar tissue is believed to represent an attempt by the body to encapsulate the injured tissue. Liver fibrosis is characterized by the accumulation of extracellular matrix that can be distinguished qualitatively from that in normal liver. Left unchecked, hepatic fibrosis progresses to cirrhosis (defined by the presence of encapsulated nodules), liver failure, and death.
As summarized by Li and Friedman (Gastroenterol. Hepatol. 14:618-633, 1999), actual and proposed therapeutic strategies for liver fibrosis include removal of the underlying cause (e.g., toxin or infectious agent), suppression of inflammation (using, e.g., corticosteroids, IL-1 receptor antagonists, or other agents), down-regulation of stellate cell activation using, e.g., gamma interferon or antioxidants), promotion of matrix degradation, or promotion of stellate cell apoptosis. Despite recent progress, many of these strategies are still in the experimental stage, and existing therapies are aimed at suppressing inflammation rather than addressing the underlying biochemical processes. Thus, there remains a need in the art for materials and methods for treating fibrosis, including liver and lung fibrosis.
Fibrotic tissues accumulate in the heart and blood vessels as a result of hypertension, hypertensive heart disease, atherosclerosis, and myocardial infarction. High blood pressure, or hypertension, can be cause by a variety of factors and often leads to the development of Hypertensive Heart Disease (HHD) with progression to cardiac arrest and myocardial infarction. Similarly, atherosclerosis and other ischemic heart diseases often also result in cardiac arrest. These cardiovascular diseases all exhibit an accumulation of extra-cellular matrix or fibrotic deposition which results in stiffening of the vasculature and stiffening of the cardiac tissue itself. This deposition of fibrotic material is a response to the damage induced by the hypertensive and/or sclerotic state, but the effects of this response also result in the negative effects of vascular and cardiac stiffening as well as ventricle enlargement. Additionally, it is believed that the increased cardiac fibrosis seen in cardiovascular disease disrupts or alters the signals transmitted to cardiomyocytes via the tissue scaffolding of the heart, further leading to disruption of efficient cardiac function and promoting cardiac arrest and myocardial infarction.